Bonding. Introduction to Bonding: Chemical bond: the force that holds two atoms together Bonds may...
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Transcript of Bonding. Introduction to Bonding: Chemical bond: the force that holds two atoms together Bonds may...
Bonding
Introduction to Bonding:Chemical bond: the force that holds two atoms together• Bonds may be formed by the
attraction of a cation to an anion ionic bond
• Bonds may be formed by sharing electrons covalent bond
Significance of Bonding
Formation of bonds (or breaking bonds) is a chemical change.Formation of bonds (or breaking bonds) is a type of reactivity.
Octet RuleOctet Rule: atoms will gain, lose, or share electrons in order to acquire the stable electron configuration of a noble gas.Try to have 8 electrons around each atom
Li + F Li F::
::
: ::
This is an example of an ionic compound
Octet RuleSince C only has 4 valence electrons, it can form more than one bond:
Note that C achieves an octet of electrons This is an example of a covalent compound
Learning Check• Draw the Lewis dot structure for
H2
• Draw the Lewis dot structure for F2
• Draw the Lewis dot structure for a water molecule, H2O
Practice Work with your partner to draw the following compounds:
CCl4 NF3H2SSiH4 O2 COCO2SO2NO2
Ionic versus Covalent Bonding
Ionic: electrical force of attraction between a cation and anion; the anion donates both electrons for the bond
cation anion
Each cation in the solid ionic compound is surrounded by anions, and each anion is surrounded by cations. Solid ionic compounds form a crystal lattice.
Na Cl
Endlessly repeating Lattice of Ions
All ionic compounds form crystal lattices, in which the positive and negative ions alternate.
stress
If the ion layers shift slightly ions with the same charge are brought side-by-side causing repulsion.
Ionic compounds have high melting and boiling points. This is due to the strong attraction of the oppositely charged ions. It takes a lot of heat energy to overcome these strong attractions.
Attractions are strongest for smaller ions or ions with greater charge (Mg 2+ O 2- vs. Na + Cl- ). These ionic compounds will have the highest melting and boiling points.
Characteristics of ionic compounds:High melting points and boiling
points (usually solid at room temp)Very hard and crystal-like;
interactions between molecules are strong
Occurs between metals and nonmetals (requires atoms to have very different electronegativity)
High polarity Conduct electricity when meltedTypically dissolve in water
Formation of Ionic Compounds Reacting Compound
Example Groups General Formula
Simple Binary Ionic Compounds Table
Covalent: sharing electrons to form a bond; each atom contributes an electron to the bond
C OC + O
Representing Covalent BondsCovalent bonds are shown by a line, representing the shared pair of electrons
CH
H
H
H
Multiple BondsCovalent compounds sometimes form multiple bonds between 2 atoms: a double bond:
O O a triple bond:
N N
Multiple BondsDouble bonds are shorter and stronger than single bondsTriple bonds are shorter and stronger than double bondsIt takes more energy to break a double or triple bond
Characteristics of covalent compounds:Low melting points and boiling points
(usually liquid or gas at room temp)Relatively soft and even flexible;
interactions between molecules are weak, allowing the molecules to move
Occurs between 2 nonmetals (requires atoms to have similar electronegativity)
Nonpolar or low polarityPoor conductors of electricity Often do not dissolve in water, but
dissolve in nonpolar liquids
Ionic, Covalent, or Polar CovalentIonic bonds form between metals and
nonmetals with large differences in electronegativity
Covalent bonds form between nonmetals with smaller differences in electronegativity
Some covalent bonds are polar. The bonding atoms have different electronegativity, causing one atom to pull the shared electrons towards it.
Polar Covalent BondsPolar covalent bonds share
electrons unequally
Polarity of Bonds
Comparison of ionic solid and covalently
bonded solidNa Cl
Ionic solid: strong electrostatic interactions
Molecular solid: weak intermolecular forces
Covalent bonds CH4
Summary